physics gcse

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P4-7: USES OF ULTRASOUND

  • ultrasound waves have a high frequency and a short wavelength which means they are able to travel inside the body - they measure the speed of blood flow in the body
  • usually used as a non-invasive way of checking babies are developing properly, but can also be used to check the patients heart, kidneys and liver
  • the waves are beamed into the body of a patient from a speciaol transmitter, these waves then reflect from different layers in the body and return at different times depending on the depth of the layer - a computer processes and develops a picture of inside the body
  • ulstrasound scans have advantages over x-ray scans as they do not damage living cells which makes them suitable for scaning unborn children. X-rays are also very penetrating and makes it difficult to see any soft tissue so ultrasound produces clearer images
  • another common use of ultrasound is to breakup kidney stones - the wave is directed at the kidney stones and this makes it vibrate at very high frequency causing it to break into pieces that are small enough to pass out the body through urine
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P4-8: RADIOACTIVITY

  • most atoms are stable, but the nucleus of some atoms are unstavle so radioactive decay occurs when the nucleus breaks down and thus emits one of the three types of ionising radiation
  • alpa particles are very ionising particles made of two protons and two neutrons ( helium atom ) they also have a positive charge
  • beta particles are fast electrons from the nucleus they have a negative charge
  • gamma rays are a high frequency electromagnetic wave and is not very ionising but travels far and is very penetrating
  • the number of radioactive decays per second is called the activity
  • alpha and beta particles and gamma ray are all ionising radiations and thus inonise the atoms of any material they pass
  • atoms are usually neutral but when they gain or lose an electron they become charged and therefore become an ion
  • when ionising radiation passes through a spark chamber it ionises the gas inside by removing some electrons this causes an electric current and a spark between metal plates
  • alpha and beta particles have a charge when they pass close to atoms they either attract or repel electrons away from the atom ionising them - alpha particles have a greater mass and therefore they are the most ionising
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